Magnetic Field Measurement Using a Step-Like GMI Sensor Combined with a Differential Circuit

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  • Nakai T.
    Industrial Technology Institute, Miyagi Prefectural Government
  • Takada K.
    Industrial Technology Institute, Miyagi Prefectural Government
  • Abe H.
    Industrial Technology Institute, Miyagi Prefectural Government
  • Hoshi N.
    NEC TOKIN Corporation
  • Suzuki H.
    NEC TOKIN Corporation
  • Ishiyama K.
    Research Institute of Electrical Communication, Tohoku University
  • Arai K. I.
    Research Institute of Electrical Communication, Tohoku University

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Other Title
  • 不連続的インピーダンス変化特性を有した薄膜ＧＭＩセンサと微分回路を組合せた磁界検出方法に関する検討
  • フレンゾクテキ インピーダンス ヘンカ トクセイ オ ユウシタ ハクマク GMI センサ ト ビブン カイロ オ クミアワセタ ジカイ ケンシュツ ホウホウ ニ カンスル ケントウ

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A giant magnetoimpedance sensor with a step-like impedance property was obtained in the case of amorphous Co85Nb12Zr3 soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a direction nearly 60 degrees relative to the width direction of the element. It was shown experimentally that the magnetic field in which the step-like impedance change occurs has an almost constant value with a standard deviation in the microtesra (μT) range. The magnetic field in which the step-like change occurs includes information on the external magnetic field. To realize a magnetic field sensor with an accuracy of nT/Hz1/2 by using this step-like phenomenon, a differential circuit was studied in combination with an alternating bias field in the kilohertz (kHz) frequency range. The aim of the differential circuit was to make the driving circuit into a digital logic circuit, by using pulse signals timed to coincide with the step-like changes. The alternating bias field increases the sampling number, because of the step-like changes in the bias frequency. The aim of the ac bias is to improve the sensor accuracy by using an averaging effect. This paper reports a first trial of the method. As a result, a high-linearity sensor without hysteresis was obtained, which had a linearity error of less than 0.5% in the range of ±100 μT. A measurement accuracy of 460 nT was achieved with a 20 Hz time constant of the output low pass filter (LPF).

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